1. Field of the Invention
The present invention relates to an oscillator, and more specifically to an oscillator provided with a feedback loop including a delay circuit.
2. Description of the Related Art
For various purposes, signal delay has been given in different electronic circuits, devices and instruments, with various methods used to give the delay. Among the delay methods currently used, a method is frequently used in which pulses of a predetermined repetition frequency are generated while a set signal is supplied. The pulses thus generated are counted and when the count value reaches a predetermined value a delay signal is generated.
Heretofore, to realize the above delay signal generating method, an oscillator is constituted of an inverted amplifier having its output connected through a delay circuit to an input of the amplifier itself. The amplifier is adapted to be put in an operable condition during a period in which a set signal is applied, and maintained in an operable condition when the set signal is not applied, thus, while the set signal is applied an oscillation signal is generated in an oscillating loop composed of the delay circuit and the amplifier in the operable condition. The oscillation signal is applied to a shaping circuit, which in turn generates a train of pulses.
With the above circuit structure, the oscillation signal is gradually magnified in amplitude from the moment the oscillation starts until the oscillation reaches a steady state. In other words, a first cycle of oscillation signal is very small. Therefore, it does not often cross a threshold level of the shaping circuit, with the result that the shaping circuit will not generate a pulse corresponding to the first cycle of the oscillation signal. This will means that a delay signal generated when the pulses outputted by the shaping circuit are counted to a predetermined number will give a time period which is longer than a desired delay time.
In addition, the length of time from the moment the set signal is applied to the moment the first pulse is generated by the shaping circuit will vary in dependence upon the temperature characteristics of the amplifier and the shaping circuit. This means that the delay time will not be a constant.